Vol 23, No 3 (2020)

In this article, author considers the process of generation of fiber modes carrying orbital angular momentum (vortex modes) using chiral fiber Bragg gratings; in this context, the formation of vortex modes is carried out by converting the fundamental mode into higher order modes. Within the framework of the article, a generalized mathematical model of chiral fiber Bragg gratings is presented, which includes an arbitrary function of apodization and chirping, which makes it possible to calculate gratings that form vortex modes of a given order for the required frequency range with the required reflection coefficient. In addition, a matrix method for describing chiral fiber Bragg gratings is proposed, based on the mathematical apparatus of the coupled modes theory and scattering matrices. This matrix approach is convenient for describing complex and / or cascaded gratings. In addition, in this work, simulation of the considered fiber structures is carried out.

Annotation – In this article, the use of the barycentric method is proposed for the numerical solution of problems of diffraction of electromagnetic waves on infinitely thin perfectly conducting screens of arbitrary shape. The numerical solution is formed in the projection formulation of the Galerkin method. The essence of the barycentric method is to form a global system of basic functions for opening the screen when determining the approximation of the desired function of the current plane on its surface. Basis functions are defined by Bernstein-type polynomials in terms of barycentric coordinates that are entered for opening the screen when it is represented as a closed simply connected polygonal region. The features of the algorithmic implementation of the barycentric method in solving diffraction problems on conducting thin screens are considered. The rate of convergence is estimated. Comparative results of calculations performed under equivalent conditions using the barycentric method and the RWG method are presented.

The problems of electrodynamic analysis of thin-wire radiating structures with double symmetry are considered. New generalized integral representations of the electromagnetic field are obtained for the case of structures with single and double symmetries. Based on the obtained expressions, mathematical models of two - and four-way elliptical spiral antennas are constructed. It is shown that taking into account double symmetry in solving the internal electrodynamic problem leads to a set of independent Fredholm integral equations of the first kind written with respect to the distributions of normal current waves, which significantly simplifies the solution of the internal electrodynamic problem. Comparisons of current distributions along conductors, their input resistance dependences on the radius of the structure, and normalized radiation patterns for two- and four-way spiral emitters are presented.

The article is devoted to features of the development two types of broadband frequency mixers with image channel suppression in the frequency range 9–27 GHz. The purpose of the study is to determine the optimal ways to solve the problem of modeling complex multifunctional microwave units. The article discusses the development process of such functional units as the local oscillator amplifier, low-noise amplifier and frequency mixer. Comparisons of the calculated characteristics with the results of measurements of the manufactured models of the samples are given. Attention is also paid to the technology of manufacturing field-effect transistors, resistors and capacitors that are part of the functional units of the frequency mixer. The scientific novelty lies in the uniqueness of the product development, which includes several functional units on one crystal. As a result, two types of frequency mixers with suppression of the mirror channel in a package design have been created, which, in terms of their characteristics, can replace similar foreign products from Analog Devices.

To reduce the crest factor in the DRM+ system due to the limitations imposed by the standard the peak limiting method (clipping) and the window weighting method, which are based on signal distortion, are widely used. As a result of the application of these methods out-of-band emissions in the signal spectrum significantly increase. After filtering out-of-band emissions the effect of a repeated increase in the crest factor appears. In this regard, there is an urgent scientific and technical problem of finding the optimal method for filtering out-of-band emissions of the DRM+ signal. The purpose of this article is to analyze the existing methods for filtering out-of-band emissions in the process of reducing the crest factor in a DRM system, as well as choosing the optimal filtering algorithm after reducing the crest factor for DRM+ transmitters. A method for suppressing out-of-band emissions using a digital filter based on FFT / IFFT is considered. The modeling of the proposed algorithm for filtering the signal by the mask of out-of-band emissions is carried out. Comparative studies of the method of the standard filtering algorithm and the proposed algorithm are carried out; the high efficiency of the latter is shown. The results obtained will improve the efficiency of reducing the crest factor in broadcasting transmitters of the DRM + standard, thereby increasing their power efficiency.

Due to the increasing complexity of radio electronic equipment, the problem of its reliability becomes much more acute. At the same time, the task of evaluating on-board equipment at the design and production stages becomes very urgent. An important issue is also the reliable determination of numerical values of its reliability indicators. Ground-based experimental testing of samples of on-board radio-electronic facilities, devices, assemblies and units facilitates the solution of this problem. In the course of this testing, various tests conducted. It been shown that the timeliest information about the quality and reliability of the equipment can be obtained from autonomous tests. In the article, the choice of an autonomous test facility has made. A microprocessor-based temperature controller chosen as an autonomous test object. The expert evaluation method used to select the object. Analysis of specifications carried out. The scope of autonomous tests was determined. An algorithm for autonomous testing of on-board radio electronic equipment of spacecraft was developed. It has properties of discreteness, determinacy, limb and mass. The development of the autonomous test algorithm takes more account of the specifics of the technology used to manufacture the product under test and the test sequence. One of the options for mathematical modelling of the process of selecting test equipment for autonomous tests been considered.